1. Field of the Invention
The invention relates to a synthetic technical yarn formed from a number of endless bicomponent filaments of the sheath-core type of which both the sheath and the core are composed of a melt-spinnable polymer. The invention also comprises a process for the manufacture of such a yarn.
2. Description of the Prior Art
A yarn of the type indicated above is known from Netherlands Patent Application No. 6 512 920. In this known yarn, the core of the filaments preferably consists of polyethylene terephthalate and the sheath of nylon 6. The yarns described in said publication were to be used for the manufacture of a reinforcing fabric for elastomeric objects, more particularly pneumatic tires for vehicles. These known yarns are virtually colourless.
For various uses, such as nets, ropes and seat-belts for vehicles there are marketed at present black technical synthetic multifilament yarns that consist essentially of polyamide-6 or polyamide-66 or of polyester. In the melt spinning process used by fiber manufacturers, such black yarns may be obtained by injecting into the melt a black pigment, more particularly carbon black particles. Alternatively, the product may be obtained by feeding polymer granules blackened with a black pigment to an extruder.
Although reasonable results may be obtained with these known black polyamide or polyester yarns, they do display several disadvantages. One of these disadvantages is the fact that during the manufacture, treatment and processing of the yarn, such as drawing, winding, twisting and the like, the black pigment present on the surface of the yarn gives rise to great wear of various more or less costly machine parts, such as rollers, guiding elements, heating elements, including hot plates or hot pins, with which the yarn comes into contact. This drawback has in the last few years become of increased importance in view of the fact that manufacturers of synthetic yarns will replace the conventional process for manufacturing technical or industrial yarns with a more integrated spin-drawing process. In the conventional process referred to the yarn is spun and wound in a first process step and drawn and wound in a second, separate process step. In said spin-drawing process, however, the above-mentioned first and second process steps are combined into a single, continuous process in which the spun yarn is drawn and wound. In order to obtain a nylon or polyester technical yarn of sufficient strength, the practice is often to draw such a yarn at a draw ratio in the range of 5 to 6. Since after the change over from the conventional process to the integrated process the same output per spinning machine will be required, the drawing operation in the spin-drawing process wil take place at considerably higher speeds than in the conventional process. The higher yarn speeds and higher yarn tension will lead to a very significant increase in the wear of machine parts and said spin-drawing of black yarns will very readily cause deep incisions in the machine parts with which the yarns come into contact. The problem of these incisions is so serious that in actual practice it makes it impossible for spun-dyed, black yarns to be made by the spin-drawing process. The incision problems caused by black pigment likewise occur in the case of a reddish pigment made up of iron oxide particles and a whitish pigment made up of titanium dioxide particles of the rutil type. It should be added that titanium dioxide of the rutil type is described on page 246 of the book "Pigments, Herstellung, Eigenschaften, Anwendung", by H. Kittel, 1960, Wissenschaftliche Verlagsgesellschaft MBH, Stuttgart, BRD.